Single crystal silicon, which is the starting material for most processes for the fabrication of semiconductor electronic devices and solar cells, is commonly prepared by the so-called Continuous Czochralski (“CCz”) or Czochralski (“Cz”) methods. In these methods, polysilicon in the form of solid feedstock material is charged to a crucible and melted, a seed crystal is brought into contact with the molten silicon or a melt, and a single crystal is grown by slow extraction.
Dopant may be added to the melt to achieve a resistivity in the silicon. Conventionally, the silicon melt is doped by feeding a dopant into the melt from a feed hopper located above the silicon melt during a dopant step.
Improper doping can lead to LZD (loss of crystalline structure) during growth of the crystal in a later process stage (e.g. crown, body, etc.). Improper doping may be caused, for example, by providing the wrong amount of dopant and/or providing the dopant at the wrong time in the process. Air (oxygen), moisture, and/or other contaminants may enter the dopant feeding system while dopant is being loaded. The introduction of air and moisture into the system should be avoided, or the air must be removed before the doping step, to prevent formation of silicon monoxide, dopant oxide, sub oxides, and other particles formed by the air and moisture reacting with the internal parts of the furnace, dopant, or the silicon charge.
A need exists for a simple, cost-effective approach to controlling the feeding of the dopant into the silicon melt to regulate the quantity of dopant, the time of feeding the dopant, and to prevent air and moisture from entering the system during the Czochralski process of growing a crystal ingot.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.